1. Field of the Invention
The present invention relates to adaptive optics and spatial light modulators for optical maskless lithography (OML) and, more specifically, to micro-electromechanical systems (MEMS) for implementing adaptive optics and/or spatial light modulators.
2. Description of the Related Art
Adaptive optics is a field of optics dedicated to the improvement of optical signals using information about signal distortions introduced by the environment in which the optical signals propagate. A representative example of an adaptive optical element is a deformable mirror driven by a wavefront sensor. An excellent introductory text on the subject is given in “Principles of Adaptive Optics” by R. K. Tyson, Academic Press, San Diego, 1991, the teachings of which are incorporated herein by reference.
Optical maskless lithography (OML) is an emerging technology intended as a replacement for conventional mask-based lithography, e.g., in low-volume production of integrated circuits. A detailed description of a representative OML system can be found, for example, in U.S. Pat. No. 5,691,541, the teachings of which are incorporated herein by reference. Briefly, instead of a permanent glass mask employed in conventional mask-based lithography, OML uses a configurable deformable mirror to project and imprint a desired image onto the substrate. Since the deformable mirror can be relatively easily reconfigured to project and imprint a new image, the cost of low-volume device production, which has largely been determined by the cost of production, inspection, repair, and protection of lithographic masks, can significantly be reduced.
One frequently used type of deformable mirror is a segmented mirror, in which each segment (pixel) can be individually translated and/or rotated. For many applications, a segmented mirror is required to have: (1) for each segment, relatively large translation and rotation magnitudes and (2) for the mirror as a whole, a fill factor of at least 98%. However, for many prior-art designs, these requirements are in direct conflict with each other and therefore difficult or even impossible to meet. For example, the high fill-factor requirement suggests a solution, in which mirror support elements and motion actuators are placed beneath (hidden under) the mirror. One result of this placement is that each segment typically rotates about an axis lying below the mirror surface and therefore is subjected to a lateral displacement within the mirror plane during rotation. To prevent physical interference with the neighboring mirror segments caused by this displacement, the spacing between the segments is increased. The latter, however, reduces the fill factor.